Heterogeneity in the response to antiretroviral drugs is well described. Pharmacologic variability may contribute to this heterogeneity and can be minimized by employing target concentration strategies. GCRC 540 is a randomized, open-label study of a safety, tolerance, and antiviral activity of a concentration-controlled regimen of zidovudine, lamivudine, and indinavir compared with the standard doses of these three agents in 40 antiretroviral-naive, HIV-infected adults with CD4 lymphocytes > 100 cells / uL and plasma H IV-RNA > 5000 copies / mL.